chore(desktop): CSS/token governance and magic-number cleanup #1046

Context

Low-risk housekeeping surfaced by an audit. CSS is otherwise well-governed
(dead CSS ≈ 0, z-index fully tokenized, 31 justified !important).

CSS structure

• theme-preview.css (670) is a grab-bag: styles bot (:420-538), About, WeChat, and
  generic form-input focus alongside actual theme-preview. Split by concern; return
  .settingsBot* to bot.css.
• Two naming dialects: kebab .maka-* everywhere vs camelCase across settings/*
  (~603 fragments). Pick one or document the settings dialect.

Token misuse / phantoms

• Hardcoded hex #07C160 (WeChat green) at theme-preview.css:550,578 — the only raw hex
  value in component CSS; tokenize as --brand-wechat or similar.
• Phantom tokens surviving on fallback only: --surface (chat-detail.css:57, real token
  is --surface-canvas), --accent-contrast (onboarding.css:319).
• Dead token defs (zero consumers): --shadow-border-opacity (maka-tokens.css:227/623),
  --radius (:383), --maka-titlebar-area-height (:537).

Magic numbers / inline styles (TS)

• Name bare delays: main.tsx:26 (150), :34 (2500); app-shell-effects.ts:139 (200);
  skills-panel.tsx:100 (4000) — sibling constants are already named.
• Collapse repeated static inline style: tool-activity.tsx:107/124/138 (+ stray
  marginRight 3 vs 4 at :147) into one class.
• session-history-list.tsx:288 — move the static transition: 140ms into CSS.

Acceptance

theme-preview split; no raw hex or phantom/dead tokens; named constants; no duplicated
static inline style. Can be done as several small PRs if preferred.